ETS Related Gene (ERG), a member of the ETS transcription family, was initially isolated and described in 1987 (Reddy et al., (1987) PROC. NATL. ACAD. SCI. USA 84:6131-35; Rao et al., (1987) SCIENCE 237: 635-39). Like other members of the ETS family, it plays a central role in mediating mitogenic signals transmitted by major cellular pathways, including the MAPK pathway. Proteins in the ETS family show a wide variety of expression patterns in human tissues. ERG is expressed in endothelial tissues, hematopoietic cells, kidney, and in the urogenital track. (Oikawa and Yamada, (2003) Gene, 303: 11-34.) Expression of ERG has also been detected in endothelial cells (microvessels) of the stroma in a small proportion of prostate cancer. (Gavrilov et al., (2001) EUR. J. CANCER, 37: 1033-40.)
The ERG protein participates in the regulation of gene expression by binding both to DNA comprising a 5′-GGA(A/T)-3′ consensus sequence and to the Jun/Fos heterodimer. These interactions occur via the highly conserved ETS domain. (Verger et al., (2001) J. BIOL. CHEM., 276: 17181-89.) Splice variants exist, and of the nine that have been reported, ERG6 and ERG9 have multiple stop codons that likely render them non-functional. (Owczarek et al., (2004) GENE, 324: 65-77.) ERG7 and ERG8 can be distinguished from ERG1-5 by the absence of exon 16. (Id.) In addition, the ERG8 transcript is unique in its inclusion of a 3′ sequence following exon 12, a portion of which forms part of the open reading frame. (Id.)
ERG, like other members of the ETS family, is a proto-oncogene with transforming activity. (Oikawa and Yamada, (2003) Gene, 303: 11-34; Hsu et al., (2004) J. Cell Biochem., 91:896-903; Reddy et al., (1987) Proc. Natl. Acad. Sci. USA, 84:6131-35; Hart et al., (1995) Oncogene, 10:1423-30; Sementchenko et al., (1998) Oncogene, 17:2883-88.) Chromosomal translocations involving ERG have been linked to Ewing sarcoma, myeloid leukemia, and cervical carcinoma. (Oikawa and Yamada, (2003) Gene, 303: 11-34.) It has recently been shown that ERG1 is the most commonly overexpressed proto-oncogene in malignant prostatic tissue. (Petrovics et al., (2005) Oncogene 24: 3847-52.) Independently, Tomlins et al., (2005) Science 310: 644-48, described novel gene fusions involving ERG and TMPRSS2, an androgen-sensitive gene, that may provide at least one possible mechanism for ERG1 overexpression. At least two additional studies have confirmed ERG rearrangements in prostate cancer. (Soller et al., (2006) Genes Chromosomes Cancer, 45:717-19; Yoshimoto et al., (2006) Neoplasia, 8: 465-69.)
Although prostate cancer is the most common non-skin cancer in North American men and the third leading cause of cancer mortality (Jemal et al., (2005) CA Cancer J. Clin., 56:106-30) remarkably little is known about critical events in prostatic carcinogenesis. While recent reports of high frequency genomic rearrangements involving the ERG locus and ERG1 overexpression are intriguing, there remains a need in the art to identify and characterize the gene expression products of the ERG locus in prostate cancer. Cancer-derived transcripts, splice variant transcripts, and altered expression ratios between transcripts are highly specific tools that can be used for cancer diagnosis throughout the different stages of cancer development. In addition, targeted inhibition or activation of these products, and/or direct manipulation of cancer-specific promoters, can be used as highly selective therapeutic strategies to target the causative root of cancer. Thus, the identification of molecular alterations specific for prostate cancer would not only permit optimization of diagnosis and prognosis but also would permit establishment of individualized treatments tailored to the molecular profile of the tumor.
In addition, while prostate cancer is increasingly detected early, the prognosis of individual patients remains a challenge. Identification of molecular biomarkers representing functionally relevant pathways that can distinguish between aggressive and indolent forms of prostate cancer at early stages will have tremendous impact in improving prognostic and therapeutic decisions. Other than serum PSA, currently there are no rational (tumor biology based) prognostic or therapeutic molecular biomarkers available in the clinical practice of prostate cancer.
While 80% of prostate cancer patients respond well to surgery, radiation therapy or watchful waiting, about 20% will develop metastasis that is often fatal to patients. Initially, prostate cancer development is driven by the androgen receptor (AR) pathway. (Heinlein et al., Endocrine Rev 25:276-308 (2004); Linja et al., J Steroid Biochem Mol Biol 92: 255-64 (2004); Shaffer et al., Lancet Oncol 4:407-14 (2003); Chen et al., Nat Med 10: 26-7 (2004).) However, frequent alterations of AR structure and/or function are well recognized during prostate cancer progression especially with metastatic disease. Other genetic pathways that are often altered in these late stage androgen-independent tumors include p53 mutations, BCL2 overexpression and mutations or reduced expression of PTEN. (Shaffer et al., Lancet Oncol 4:407-14 (2003).) Importantly, both p53 and PTEN pathways may affect AR functions.
Defects in AR-mediated signaling are increasingly highlighted for potential causal roles in prostate cancer progression. (Heinlein et al., Endocrine Rev 25:276-308 (2004); Dehm et al., J Cell Biochem 99: 333-344 (2006).) Prostate cancer associated alterations of AR functions by various mechanisms, including AR mutations, AR gene amplification, altered AR mRNA or AR protein levels, changes in AR interaction with co-activators/co-repressors and ligand independent AR activation by growth factors/cytokines, may all contribute to prostate cancer progression. (Gelmann E P. J Clin Oncol 20:3001-15 (2002); Grossman et al., J Natl Cancer Inst 93: 1687-97 (2001).) Due to the lack of precise knowledge of AR dysfunctions in pathologic specimens, it is difficult to identify patients with functional defects of AR.
The choice of therapy for late stage prostate cancer is systemic androgen ablation, which eventually fails in most patients. Therefore, the knowledge of AR pathway dysfunctions that are predictive of androgen ablation therapy failure would significantly impact the patient stratification for new emerging therapeutic strategies.
Unlike in breast cancer where estrogen receptor protein status in primary tumor is effectively used in making therapeutic and prognostic decisions (Yamashita et al., Breast Cancer 13(1):74-83 (2006); Martinez et al., Am J Surg. 191(2):281-3 (2006); Giacinti et al., Oncologist 11(1):1-8 (2006); Regan et al., Breast 14(6):582-93(2005); Singh et al., J Cell Biochem. 96(3):490-505 (2005)), AR protein expression status does not appear to be useful in prostate cancer, likely because many factors besides AR protein expression level may affect AR activity. Although AR expression can be detected throughout the progression of prostate cancer, it is heterogeneous and changes over time. Several studies have indicated that AR expression is reduced in poorly differentiated areas with higher Gleason score. (Heinlein et al., Endocrine Rev 25:276-308 (2004); Linja et al., J Steroid Biochem Mol Biol 92: 255-64 (2004); Shaffer et al., Lancet Oncol 4:407-14 (2003); Chen et al., Nat Med 10: 26-7 (2004); Gelmann E P. J Clin Oncol 20:3001-15 (2002); Grossman et al., J Natl Cancer Inst 93: 1687-97 (2001); Krishnan et al., Clin Cancer Res 6:1922-30 (2000).) In contrast, some recent reports found that higher AR expression is associated with higher clinical stage, higher Gleason score, and with decreased PSA recurrence-free survival. (Linja et al., Cancer Res 61:3550-55 (2001); Sweat et al., J Urol 161:1229-32 (1999); Li et al., Am J Surg Pathol 28:928-34 (2004).) Part of the reason for this controversy is the inherent heterogeneity of AR expression in the prostate and the semi-quantitative nature of immunohistochemical evaluations. (Krishnan et al., Clin Cancer Res 6:1922-30 (2000).) In recent years, our laboratory has established novel insights into the androgen regulated transcriptome and identified AR targets which have promise in defining the role of AR dysfunctions in prostate cancer, as well as in providing novel biology based biomarkers and therapeutic targets during prostate cancer progression. (Xu et al., Cancer Res. 63(15):4299-304 (2003); Segawa et al., Oncogene 21(57):8749-58 (2002); Xu et al., Int J Cancer 92(3):322-8 (2001); Xu et al., Genomics 66(3): 257-263 (2000); Masuda et al., J Mol Biol. 353(4):763-71 (2005); Richter et al., Prostate Cancer Prostatic Dis. 2007 Feb. 13; [Epub ahead of print].)
Nevertheless, a need still exists to streamline the functional evaluation of AR defects at early stages of prostate cancer, when the impact of this knowledge on disease management will be more profound. The present application meets this need by providing a read out for the measurement of the expression of carefully selected AR downstream targets. This read out provides information on the in vivo functional status of AR in prostate cancer cells, which helps to stratify patients based on AR signal amplitude and can be used to help prognose prostate cancer and provide new ways of managing and treating these patients.
Citation of references herein shall not be construed as an admission that such references are prior art to the present invention.